This invention relates to multilayer films used as appliques, for example, for paint replacement applications.
Paint on an aircraft can serve to protect the outer surface as well as to provide decorative features. Paint is applied in a controlled environment to alleviate environmental and health hazards, which results in significantly high costs. Current aircraft paint technology uses large volumes of volatile organic compounds for application and removal, such as methylene chloride and methyl ethyl ketone, and heavy metals, such as chromium. Such materials are potentially hazardous to workers and the environment. As a result, there is a desire to eliminate the need to paint aircraft.
Over the past 30 years, tapes have been used to protect aircraft substrates as an alternative to paint systems. For example, polyurethane tapes have been used to protect aircraft leading edge substrates from damage from rain, sand, sleet, and other airborne particle damage. Cushioned versions of polyurethane tapes have been used to absorb the impact energy of small rocks and debris and provide protection for antennas, fuselage panels, and composite wing flaps. Thin film tapes capable of being printed with graphics have been used for aircraft markings and decals. Such tapes include polymer backings and adhesives that have significant advantages; however, they are typically limited in their applications because few environments are as demanding as the exterior of an aircraft due to temperature variances, fluid exposures, conformance to various contoured and/or complex surfaces, etc. Thus, a need exists for paint replacement technologies that can withstand the harsh environments to which aircraft are exposed while maintaining acceptable film appearance characteristics (specifically, high gloss retention, gouge and scratch resistance) and can be used on the entire surface of the aircraft.
The present invention provides an applique that comprises a fluorinated polymer backing having two treated surfaces and having an adhesive layer on one treated surface and a cured urethane coating layer on the other treated surface, the cured urethane coating layer comprising urethane polymer and optionally, additives such as colorants, UV absorbers, etc. The adhesive preferably is a pressure-sensitive adhesive which preferably comprises an acrylate copolymer comprising at least one monofunctional alkyl (meth)acrylate monomer (also known as a xe2x80x9crepeat unitxe2x80x9d when describing a copolymer) and at least one monofunctional free-radically copolymerizable acid-containing reinforcing monomer whose homopolymer glass transition temperature is higher than that of the alkyl (meth)acrylate homopolymer.
In another embodiment of the present invention, an applique comprises a fluorinated polymer backing that is not perfluorinated, an adhesive layer on one treated surface of the backing and a cured urethane coating layer on the other treated surface, the cured urethane coating layer comprising urethane polymer, and optionally, additives such as colorants, UV absorbers, etc. The adhesive is preferably a pressure-sensitive adhesive which preferably comprises an acrylate copolymer comprising at least one monofunctional alkyl (meth)acrylate monomer and at least one monofunctional free-radically copolymerizable acid-containing reinforcing monomer whose homopolymer glass transition temperature is higher than that of the alkyl (meth)acrylate homopolymer.
The present invention also provides an airplane comprising an outer surface and an applique thereon, wherein the applique comprises a fluorinated polymer backing having two treated surfaces, an adhesive layer on one treated surface and a cured urethane coating layer on the other treated surface, the cured urethane coating layer comprising urethane polymer and, optionally additives such as colorants, UV absorbers, etc. The adhesive is preferably a pressure-sensitive adhesive and preferably comprises an acrylate copolymer comprising copolymerized monomers comprising at least one monofunctional alkyl (meth)acrylate monomer and at least one monofunctional free-radically copolymerizable acid-containing reinforcing monomer having a homopolymer glass transition temperature higher than that of the alkyl (meth)acrylate homopolymer.
The appliques of the invention have a gloss retention of greater than or equal to 10 percent, preferably greater than or equal to 30 percent, more preferably greater than or equal to 40 percent, as measured at an angle of 60xc2x0 with respect to the applique surface and greater than or equal to 30 percent, preferably greater than or equal to 45 percent, more preferably greater than or equal to 60 percent, as measured at an angle of 85xc2x0 with respect to the applique surface for glossy and semi-glossy surfaces.
Preferably, the initial gloss is greater than 10, more preferably 35 or greater, even more preferably, 40 or greater, and even more preferably 50 or greater when measured at an angle of 60xc2x0 with respect to the applique surface. The appliques of the invention are also both conformable and removable and exhibit resistance to hydrocarbon fluids. Preferably, the applique of the present invention exhibits resistance to hydraulic fluids and has a film hardness of greater than or equal to 6B.
Appliques of the present invention preferably provide a uniform coating thickness having a tight tolerance; for example, a cured urethane coating layer having a thickness of 52.1 micrometers may have a tolerance of plus or minus 1.5 micrometers. Preferably, the coating thickness of the cured urethane coating layer may range from about 12 micrometers to about 254 micrometers. The adhesive is preferably a pressure-sensitive adhesive which preferably comprises an acrylate copolymer having at least one monofunctional alkyl (meth)acrylate monomer and at least one monofunctional free-radically copolymerizable acid-containing reinforcing monomer whose homopolymer glass transition temperature is higher than that of the alkyl (meth)acrylate monomer.
Advantages of the appliques of the invention include: improved gloss retention and improved gouge and scratch resistance as compared to fluoropolymer backing alone; and the appliques are more easily removable from substrates than conventional paints so that the appearance of the substrate may be changed as desired with less labor than required with conventional paints.
The present invention is directed to appliques, particularly appliques for replacing paint on substrates. Such appliques are useful on vehicles, such as planes, trains, and automobiles, boats, and ships. They can be used on painted, primed (e.g., epoxy primer, chromated primer), or bare surfaces. They can be used on metal surfaces, particularly aluminum surfaces, which can be an anodized surface, a chromate-treated surface (which results from treatment with Alodine 1200, available from Amchem Products, Inc., Abmoler, Pa., or otherwise treated surface. They can be used on surfaces of composite materials, such as carbon fiber reinforced plastics, for example.
The appliques of the present invention can be in a variety of shapes, sizes, and thicknesses. They can be in the form of sheet materials or they can be in the form of three-dimensional shaped articles, such as a thermal-formed boot. Such three-dimensional shaped appliques can be used on the wingtip or nose of an airplane, for example. If in the form of a sheet material, the applique typically has a thickness of about 12-760 micrometers, whereas if in the form of a three-dimensional object, the applique typically has a thickness of about 170-760 micrometers.
The appliques of the present invention can be used as decals and decorative appliques or they can be used as protective appliques to reduce corrosion, gouge, and scratch damage, for example. They can be used in multiple layers, such as a protective applique over a decal or a decal over a protective applique, for example. Significantly, the appliques of the present invention can be used to completely cover the exterior surface of a vehicle, such as an airplane, as a replacement for paint, as a protective coating over paint, or as a coating under paint. They can be applied such that the edges of the appliques overlap or form butt joints.
Appliques of the present invention exhibit a glossy appearance and provide excellent gloss retention over the range of glossy and semi-glossy surfaces. By this, it is meant that an applique of the present invention has an initial gloss of greater than 10 when measured at an angle of 60xc2x0, and a gloss retention of greater than or equal to 10 percent as measured at an angle of 60xc2x0 and greater than or equal to 30 percent as measured at an angle of 85xc2x0, both angles being with respect to the surface of the applique. As used herein, the term xe2x80x9cglossyxe2x80x9d is used to encompass both semi-glossy and glossy appearing surfaces. Such surfaces are defined as those that exhibit an initial gloss value of greater than 10 when measured at an angle of 60xc2x0. A glossy surface may be described as one having luster or brightness. Semi-glossy may be described as between glossy and or matte. A flat surface may be described as free from gloss. A matte surface may be described as a surface having an initial gloss of 10 or less when measured at an angle of 60xc2x0.
The appliques of the invention also preferably have a film hardness of greater than or equal to 6B and are both conformable and removable.
The appliques of the present invention are stable under a wide variety of environmental conditions, including wide ranges of temperature and humidity, and when exposed to moisture and fluids. That is, the appliques of the present invention are preferably conformable, fluid-resistant, and adhere well to a variety of surfaces under a variety of conditions. As used herein, a xe2x80x9cconformablexe2x80x9d applique is one that can be applied to various contoured and/or complex surfaces and maintains intimate contact with the entire surface for the time required for the desired application. Preferably, a conformable applique passes the conformability test described in the examples below.
Appliques of the present invention are also resistant to hydrocarbon fluids (e.g., jet fuel). Preferably appliques of the present invention have a peel strength of at least about 30 N/100 mm at room temperature after being applied to an aluminum substrate and immersed in a hydrocarbon fluid for 14 days at room temperature. More preferably, the peel strength is at least about 35 N/100 mm, after such exposure.
Preferably, appliques of the present invention are also resistant to phosphate ester hydraulic fluids (e.g., SKYDROL hydraulic fluid). Preferably, appliques of the present invention have a peel strength of at least about 25 N/100 mm at room temperature after being applied to an aluminum substrate and immersed in a phosphate ester hydraulic fluid for 30 days at room temperature. More preferably, the peel strength is at least about 35 N/100 mm after such exposure.
The appliques of the present invention are expected to exhibit the hydrocarbon and hydraulic fluid resistance described above based on the performance of the applique constructions described in WO 99/64235, filed Jun. 6, 1998.
Preferably, appliques of the present invention exhibit significant peel strength at low temperatures. By this it is meant that an applique of the present invention has a peel strength of at least about 30 N/100 mm at xe2x88x9251xc2x0 C. More preferably, the peel strength is at least about 40 N/100 mm, and even more preferably, the peel strength is at least about 60 N/100 mm at xe2x88x9251xc2x0 C.
An applique according to the present invention includes a backing having both major surfaces treated and having an adhesive layer, preferably, a pressure-sensitive adhesive layer, on the first major treated surface and a urethane coating layer on the second major treated surface. The backing includes a fluorinated polymer, preferably, one that is not perfluorinated. The pressure-sensitive adhesive preferably includes an acrylate copolymer, preferably, a crosslinked acrylate copolymer. Significantly, and surprisingly, appliques of the present invention can withstand the harsh environments to which aircraft are exposed while retaining high gloss and preventing gouge and scratch damage and are also conformable and removable. This allows the applique of the present invention to be used on the entire surface of an aircraft.
Backing
Backings of the appliques of the present invention include one or more fluorinated polymers. Herein, a polymer includes homopolymers and copolymers. Copolymers include polymers containing two or more different monomers, including terpolymers, tetrapolymers, etc. Preferably, the fluorinated polymers are prepared from olefinically unsaturated monomers. Also, preferably, the fluorinated polymers are not perfluorinated. That is, although they may be made from perfluorinated monomers, the resultant polymers have both Cxe2x80x94H and Cxe2x80x94F bonds, for example.
Preferably, fluorinated polymers suitable for use in making backings for appliques of the present invention are those that form conformable, fluid-resistant sheet materials. As used herein, a xe2x80x9cconformablexe2x80x9d backing is one that can be applied to various contoured and/or complex surfaces and maintains intimate contact with the entire surface for the time required for the desired application. Preferably, a conformable backing passes the conformability test described in the examples below.
One class of useful fluorinated polymers include interpolymerized units derived from vinylidene fluoride (also referred to as xe2x80x9cVF2xe2x80x9d or xe2x80x9cVDFxe2x80x9d). Such materials typically include at least about 3 weight percent of interpolymerized units derived from VF2, which may be homopolymers or copolymers with other ethylenically unsaturated monomers, such as hexafluoropropylene (xe2x80x9cHFPxe2x80x9d), tetrafluoroethylene (xe2x80x9cTFExe2x80x9d), chlorotrifluoroethylene (xe2x80x9cCTFExe2x80x9d), 2-chloropentafluoropropene, perfluoroalkyl vinylethers, perfluorodiallylether, perfluoro-1,3-butadiene, and the like. Such fluorine-containing monomers may also be copolymerized with fluorine-free terminally unsaturated olefinic comonomers, such as ethylene or propylene. Preferred such fluoropolymers include tetrafluoroethylene-hexafluoropropylene-vinylidene fluoride terpolymers and hexafluoropropylene-vinylidene fluoride copolymers. Commercially available fluoropolymer materials of this type include, for example, THV 200, THV 400, and THV 500 fluoropolymers, which are available from Dyneon (a wholly owned subsidiary of Minnesota Mining and Manufacturing Company), Oakdale, Minn., and SOLEF 11010, which is available from Solvay Polymers Inc., Houston, Tex.
Another class of useful fluorinated polymers include interpolymerized units derived from one or more of hexafluoropropylene (xe2x80x9cHFPxe2x80x9d), tetrafluoroethylene (xe2x80x9cTFExe2x80x9d), chlorotrifluoroethylene (xe2x80x9cCTFExe2x80x9d), and/or other perhalogenated monomers and further derived from one or more hydrogen-containing and/or non-fluorinated olefinically unsaturated monomers. Useful olefinically unsaturated monomers include alkylene monomers, such as ethylene, propylene, 1-hydropentafluoropropene, 2-hydropentafluoropropene, etc. A preferred such fluoropolymer is a copolymer of poly(tetrafluoroethylene) and ethylene. Commercially available fluoropolyiner materials of this type include, for example, TEFZEL LZ300 fluoropolymers, which is available from DuPont Films, Buffalo, N.Y.
Other useful fluorinated polymers, preferably nonperfluorinated polymers, include poly(vinylfluoride), such as TEDLAR TAW15AH8, which is available from DuPont Films. Blends of fluoropolymers can also be used to make the backings for the appliques of the present invention. For example, blends of two different types of nonperfluorinated fluoropolymers can be used, as well as blends of a nonperfluorinated fluoropolymer with a perfluorinated fluoropolymer. Furthermore, blends of fluoropolymers with nonfluoropolymers, such as polyurethane and polyethylene, for example, can also be used, as long as one of the polymers in the blend is a fluoropolymer, and the nonfluoropolymer is used in a minor amount. Fluoropolymer backings for use in the present invention can be made using a variety of methods, including cast and extrusion methods, preferably, however, they are extruded.
The backings are typically in the form of sheet materials having two major surfaces. Typically, both of the surfaces are treated to allow for bonding of the adhesive and urethane layer. Such treatment methods include corona treatment, particularly corona discharge in an atmosphere containing nitrogen, or nitrogen and hydrogen, as disclosed in U.S. Pat. No. 5,972,176 (Seth et al.). Another useful treatment method includes a chemical etch using sodium naphthalenide. Such treatment methods are disclosed in Polymer Interface and Adhesion, Souheng Wu, Ed., Marcel Dekker, Inc., NY and Basel, pages 279-336 (1982), and Encyclopedia of Polymer Science and Engineering, Second Edition, Supplemental Volume, John Wiley and Sons, pages 674-689 (1989). Another useful treatment method is the FLUOROTECH process, available from Acton Industries, Inc., Pittston, Pa. Other treatment methods include the use of such materials as primers. These may be employed either in place of, or in addition to the surface treatments described above. An example of a useful primer is ADHESION PROMOTER #86A (a liquid primer, available from Minnesota Mining and Manufacturing Company, St. Paul, Minn.)
Treatment conditions are sufficient if a peel adhesion strength of 30 N/100 mm is obtained when tested at a temperature of xe2x88x9251xc2x0 C. as described in xe2x80x9cPeel Adhesion Strength (Method B)xe2x80x9d below.
The backings may be clear and colorless, or preferably include a colorant, such as a pigment or dye. Preferably, the colorant is an inorganic pigment, such as those disclosed in U.S. Pat. No. 5,132,164 (Moriya et al.). The pigment may be incorporated into one or more non-fluorinated polymers, which can be blended with one or more fluorinated polymers.
Adhesive
The backing of the present invention may be adhered to a substrate using adhesives such as room temperature pressure-sensitive adhesives (PSA), hot melt PSAs, or thermoplastics. Preferably, the adhesive is a room temperature PSA. An example of a room temperature PSA is an acrylate pressure-sensitive adhesive. Such materials possess a four-fold balance of adhesion, cohesion, stretchiness, and elasticity, and a glass transition temperature (Tg) of less than about 20xc2x0 C. Thus, they are tacky to the touch at room temperature (e.g., about 20xc2x0 C. to about 25xc2x0 C.), as can be determined by a finger tack test or by conventional measurement devices, and can easily form a useful adhesive bond with the application of light pressure. An acceptable quantitative description of a pressure-sensitive adhesive is given by the Dahlquist criterion line (as described in the Handbook of Pressure Sensitive Adhesive Technology, Second Edition, D. Satas, ed., Van Nostrand Reinhold, New York, N.Y., pages 171-176 (1989)), which typically indicates that materials having a storage modulus (Gxe2x80x2) of less than about 3xc3x97105 Pascals (measured at 10 radian/second at a temperature of about 20xc2x0 C. to about 22xc2x0 C.) have pressure-sensitive adhesive properties while materials having a Gxe2x80x2 in excess of this value do not. As stated above, the acrylate pressure-sensitive adhesive copolymers used herein are surprisingly advantageous because they show desirable adhesive properties over a broad temperature range, particularly at low temperatures, to a wide variety of substrates. In addition, they show desirable adhesive properties even after exposure to various fluids.
Preferred poly(acrylates) are derived from: (A) at least one monofunctional alkyl (meth)acrylate monomer (i.e., alkyl acrylate and alkyl methacrylate monomer); and (B) at least one monofunctional free-radically copolymerizable acid-containing reinforcing monomer. The reinforcing monomer has a homopolymer glass transition temperature (Tg) higher than that of the alkyl (meth)acrylate homopolymer and is one that increases the glass transition temperature and modulus of the resultant copolymer. Herein, xe2x80x9ccopolymerxe2x80x9d refers to polymers containing two or more different monomers, including terpolymers, tetrapolymers, etc.
Preferably, the monomers used in preparing the pressure-sensitive adhesive copolymers of the present invention include: component (A)xe2x80x94a monofunctional alkyl (meth)acrylate monomer that, when homopolymerized, generally has a glass transition temperature of no greater than about 0xc2x0 C.; and component (B)xe2x80x94a monofunctional free-radically copolymerizable acid-containing reinforcing monomer that, when homopolymerized, generally has a glass transition temperature of at least about 10xc2x0 C. The glass transition temperatures of the homopolymers of monomers A and B are typically accurate to within xc2x15xc2x0 C. and are measured by differential scanning calorimetry.
Monomer A, which is a monofunctional alkyl acrylate or methacrylate (i.e., (meth)acrylic acid ester), contributes to the flexibility and tack of the copolymer. Preferably, monomer A has a homopolymer Tg of no greater than about 0xc2x0 C. Preferably, the alkyl group of the (meth)acrylate has an average of about 4 to about 20 carbon atoms, and more preferably, an average of about 4 to about 14 carbon atoms. The alkyl group can optionally contain oxygen atoms in the chain thereby forming ethers or alkoxy ethers, for example. Examples of monomer A include, but are not limited to, 2-methylbutyl acrylate, isooctyl acrylate, lauryl acrylate, 4-methyl-2-pentyl acrylate, isoamyl acrylate, sec-butyl acrylate, n-butyl acrylate, n-hexyl acrylate, 2-ethylhexyl acrylate, n-octyl acrylate, isooctyl acrylate, n-decyl acrylate, isodecyl acrylate, isodecyl methacrylate, and isononyl acrylate. Other examples include, but are not limited to, poly-ethoxylated or -propoxylated methoxy (meth)acrylate (i.e., poly(ethylene/propylene oxide) mono-(meth)acrylate) macromers (i.e., macromolecular monomers), polymethylvinyl ether mono(meth)acrylate macromers, and ethoxylated or propoxylated nonyl-phenol acrylate macromers. The molecular weight of such macromers is typically about 100 grams/mole to about 600 grams/mole, and preferably, about 300 grams/mole to about 600 grams/mole. Preferred monofunctional (meth)acrylates that can be used as monomer A include 2-methylbutyl acrylate, isooctyl acrylate, lauryl acrylate, and poly(ethoxylated) methoxy acrylate (i.e., methoxy terminated poly(ethylene glycol) mono-acrylate or poly(ethyleneoxide) monomethacrylate). Combinations of various monofunctional monomers categorized as an A monomer can be used to make the pressure-sensitive copolymer used in making the appliques of the present invention.
Monomer B, which is a monofunctional free-radically copolymerizable acid-containing reinforcing monomer increases the glass transition temperature of the copolymer. As used herein, xe2x80x9creinforcingxe2x80x9d monomers are those that increase the modulus of the adhesive, and thereby its strength. Preferably, monomer B has a homopolymer Tg of at least about 10xc2x0 C. As used herein, xe2x80x9cacid-containingxe2x80x9d monomers are those that include acid functionality such as an acrylic acid or a methacrylic acid functionality. Examples of monomer B include, but are not limited to, acrylic acid and methacrylic acid, itaconic acid, crotonic acid, maleic acid, and fumaric acid. A preferred reinforcing monofunctional acrylic monomer that can be used as monomer B includes acrylic acid and methacrylic acid. Combinations of various reinforcing monofunctional monomers categorized as a B monomer can be used to make the copolymer used in making the protective appliques of the present invention.
Optionally, if desired, the copolymer can also include a monofunctional free-radically copolymerizable neutral or nonpolar reinforcing monomer in addition to the acid-containing monomer. Examples of such monomers include, but are not limited to, 2,2-(diethoxy)ethyl acrylate, hydroxyethyl acrylate or methacrylate, 2-hydroxypropyl acrylate or methacrylate, methyl methacrylate, isobutyl acrylate, n-butyl methacrylate, norbornyl acrylate, isobornyl acrylate, 2-(phenoxy)ethyl acrylate or methacrylate, biphenylyl acrylate, t-butylphenyl acrylate, cyclohexyl acrylate, dimethyladamantyl acrylate, 2-naphthyl acrylate, phenyl acrylate, and N-vinyl pyrrolidone. Combinations of such neutral reinforcing monofunctional monomers can be used to make the copolymer used in making the appliques of the present invention.
The acrylate copolymer is preferably formulated to have a resultant Tg of less than about 25xc2x0 C. and more preferably, less than about 0xc2x0 C. Such acrylate copolymers preferably include about 80 weight percent to about 96 weight percent of at least one alkyl (meth)acrylate repeat unit and about 4 weight percent to about 20 weight percent of at least one copolymerizable acid-containing reinforcing repeat unit. More preferably, the acrylate copolymers about 85 weight percent to about 95 weight percent of at least one alkyl (meth)acrylate repeat unit and about 6 weight percent to about 15 weight percent of at least one copolymerizable acid-containing reinforcing repeat unit. These weight percentages are based on the total weight of the monomers.
One or more nonionic crosslinking agents that may, or may not, be copolymerizable with monomers A and B, can be used in the pressure-sensitive adhesives of the appliques of the present invention if desired. A crosslinking agent is referred to herein as component C. Typically, component C modifies the adhesion of the pressure-sensitive adhesive and improves its cohesive strength. The crosslinking agent typically produces chemical crosslinks (e.g., covalent bonds). Prior to application of the applique to a substrate, the crosslinking functionality is consumed, i.e., it is essentially completely reacted with monomers A and B or copolymers thereof.
When component C contains ethylenic unsaturation, it is incorporated into the backbone of the copolymer by copolymerization with monomers A and B through the ethylenic unsaturation. Such crosslinking agents are disclosed in U.S. Pat. No. 4,379,201 (Heilmann et al.); U.S. Pat. No. 4,737,559 (Kellen et al.); U.S. Pat. No. 5,073,611 (Rehmer et al.); and U.S. Pat. No. 5,506,279 (Babu et al.). Alternatively, component C can be essentially independent of the polymeric backbone. Materials of this type can cause crosslinking by, for example, reaction with the pendant carboxylic acid group of monomer B as disclosed in U.S. Pat. No. 5,604,034 (Matsuda), or by photoactivated hydrogen abstraction as disclosed in U.S. Pat. No. 4,330,590 (Vesley) and U.S. Pat. No. 4,329,384 (Vesley). Matsuda discloses the use of multifunctional crosslinking agents whose functionalities are reactive with carboxylic acid groups, while Vesley describes additives that can cause crosslinking upon exposure to ultraviolet radiation (e.g., radiation having a wavelength of about 250 nanometers to about 400 nanometers).
Preferably, component C is (1) a copolymerizable olefinically unsaturated compound, which, in the excited state, is capable of abstracting hydrogen; (2) a compound having at least two reactive functional groups reactive with carboxylic acid groups; or (3) a noncopolymerizable compound which, in the excited state, is capable of abstracting hydrogen. Component C1 is a free-radically polymerizable monomer capable of polymerizing with monomers A and/or B. Components C2 and C3 are essentially free of olefinic unsaturation and thus typically not copolymerizable with monomers A and/or B. Combinations of various crosslinking agents can be used to make the pressure-sensitive adhesive of the present invention.
One type of nonionic crosslinking agent (i.e., component C1) is an olefinically unsaturated compound that is copolymerized with monomers A and B and generates free radicals on the polymer upon irradiation of the polymer. Examples of such a compound include an acrylated benzophenone as described in U.S. Pat. No. 4,737,559 (Kellen et al.), p-acryloxy-benzophenone, which is available from Sartomer Company, Exton, Pa., and monomers described in U.S. Pat. No. 5,073,611 (Rehmer et al.) including p-N-(methacryloyl4-oxapentamethylene)-carbamoyloxybenzophenone, N-(benzoyl-p-phenylene)-Nxe2x80x2-(methacryloxymethylene)-carbodiimide, and p-acryloxy-benzophenone. U.S. Pat. No. 5,506,279 (Babu et al.) at columns 5-6, describes another suitable olefinically unsaturated crosslinking agent referred to therein as Formula 2, which is {2-[4-(2-hydroxy-2-methyl-propan-1-one)phenoxy]}ethyl(2-methyl-2-(2-methyl-2-propen-1-one)amino)propanoate. The olefinically unsaturated compound which, in the excited state, is capable of abstracting hydrogen preferably includes acrylic functionality. Combinations of such crosslinking agents can be used to make the pressure-sensitive adhesive used in the present invention.
A second type of nonionic crosslinking agent (i.e., component C2) is a crosslinking compound which is essentially free of olefinic unsaturation and is capable of reacting with the carboxylic acid groups of monomer B. It includes at least two functional groups reactive with carboxylic acid groups. It may be added to a mixture of monomers A and B prior to their polymerization, or after they have been formed into a partially polymerized syrup, or to a copolymer of monomers A and B. Examples of such components include, but are not limited to, 1,4-bis(ethyleneiminocarbonylamino)benzene; 4,4-bis(ethyleneiminocarbonylamino)diphenylmethane; 1,8-bis(ethyleneiminocarbonylamino)octane; 1,4-tolylene diisocyanate; and 1,6-hexamethylene diisocyanate as described in U.S. Pat. No. 5,604,034 (Matsuda). Another example is N,Nxe2x80x2-bis-1,2-propyleneisophthalamide as described in U.S. Pat. No. 4,418,120 (Kealy et al.). Other such crosslinking agents are available from K. J. Quin and Co., Seabrook, N.H., and EIT Inc., Lake Wyllie, S.C. Other examples of C2 crosslinking agents include diepoxides, dianhydrides, bis(amides), and bis(imides). Combinations of such crosslinking agents can be used to make the pressure-sensitive adhesive used in the present invention.
A third type of nonionic crosslinking agent (i.e., component C3) is a compound which is essentially free of olefinic unsaturation, is noncopolymerizable with monomers A and B, and, in the excited state, is capable of abstracting hydrogen. It is added to a copolymer of monomers A and B, or a partially polymerized syrup of monomers A and B. Upon irradiation of the mixture, component C3 generates free radicals on the polymer or partially polymerized material. Examples of such components include, but are not limited to, 2,4-bis(trichloromethyl)-6-(4-methoxy)phenyl)-s-triazine; 2,4-bis(trichloromethyl)-6-(3,4-dimethoxy)phenyl)-s-triazine; 2,4-bis(trichloromethyl)-6-(3,4,5-trimethoxy)phenyl)-s-triazine; 2,4-bis(trichloromethyl)-6-(2,4-dimethoxy)phenyl)-s-triazine; 2,4-bis(trichloromethyl)-6-(3-methoxy)phenyl)-s-triazine as described in U.S. Pat. No. 4,330,590 (Vesley), and 2,4-bis(trichloromethyl)-6-naphthenyl-s-triazine and 2,4-bis(trichloromethyl)-6-(4-methoxy)naphthenyl-s-triazine as described in U.S. Pat. No. 4,329,384 (Vesley). Combinations of such crosslinking agents can be used to make the pressure-sensitive adhesive used in the present invention.
Another type of crosslinking agent that can be used in addition to one or more of components C1-C3, is an acrylic crosslinking monomer (component C4) containing at least two acrylic moieties, which preferably has an average of less than about 12 atoms in the chain between acrylic groups. Examples of this type of crosslinking agent include, but are not limited to, trimethylolpropane triacrylate, 1,6-hexanediol diacrylate, pentaerythritol tetraacrylate, 1,2-ethylene glycol diacrylate, dodecyl diacrylate, and the diacrylate of ethylene oxide modified bisphenol A.
If used, the crosslinking agent is used in an effective amount, by which is meant an amount that is sufficient to cause crosslinking of the pressure-sensitive adhesive to provide adequate cohesive strength to produce the desired final adhesion properties to the substrate of interest. Preferably, if used, the crosslinking agent is used in an amount of about 0.01 part to about 2 parts by weight, based on 100 parts of the copolymer.
If a photocrosslinking agent has been used, the adhesive can be exposed to ultraviolet radiation having a wavelength of about 250 nm to about 400 nm. The radiant energy in this preferred range of wavelength required to crosslink the adhesive is about 100 millijoules/centimeter2 (mJ/cm2) to about 1,500 mJ/cm2, and more preferably, about 200 mJ/cm2 to about 800 mJ/cm2.
Preparation of Acrylate Copolymers
The acrylate pressure-sensitive adhesives of the present invention can be synthesized by a variety of free-radical polymerization processes, including solution, radiation, bulk, dispersion, emulsion, and suspension polymerization processes. Polymerization of the monomers to form the copolymer useful in the pressure-sensitive adhesive composition of the present invention is typically carried out using thermal energy, electron-beam radiation, ultraviolet radiation, and the like. Such polymerizations can be facilitated by a polymerization initiator, which can be a thermal initiator or a photoinitiator. Examples of suitable photoinitiators include, but are not limited to, benzoin ethers such as benzoin methyl ether and benzoin isopropyl ether, substituted benzoin ethers such as anisoin methyl ether, substituted acetophenones such as 2,2-dimethoxy-2-phenylacetophenone, and substituted alpha-ketols such as 2-methyl-2-hydroxypropiophenone. Examples of commercially available photoinitiators include IRGACURE 651 and DAROCUR 1173, both available from Ciba-Geigy Corp., Hawthorne, N.Y., and LUCERIN TPO from BASF, Parsippany, N.J. Examples of suitable thermal initiators include, but are not limited to, peroxides such as dibenzoyl peroxide, dilauryl peroxide, methyl ethyl ketone peroxide, cumene hydroperoxide, dicyclohexyl peroxydicarbonate, as well as 2,2-azo-bis(isobutryonitrile), and t-butyl perbenzoate. Examples of commercially available thermal initiators include VAZO 64, available from ACROS Organics, Pittsburgh, Pa., and LUCIDOL 70, available from Elf Atochem North America, Philadelphia, Pa. The polymerization initiator is used in an amount effective to facilitate polymerization of the monomers. Preferably, the polymerization initiator is used in an amount of about 0.1 part to about 5.0 parts by weight, and more preferably, about 0.2 part to about 1.0 part by weight, based on 100 parts of the copolymer.
If a photocrosslinking agent is used, the coated adhesive can be exposed to ultraviolet radiation having a wavelength of about 250 nm to about 400 nm. The radiant energy in this preferred range of wavelength required to crosslink the adhesive is about 100 millijoules/cm2 to about 1,500 millijoules/cm2, and more preferably, about 200 nmillijoules/cm2 to about 800 millijoules/cm2.
The copolymers of the present invention can be prepared by a variety of techniques, which may or may not include solvent or chain transfer agents (e.g., CBr4) to control molecular weight. These techniques may involve the use of appropriate polymerization initiators. A preferred solvent-free polymerization method using monomers A, B, and a crosslinking agent is disclosed in U.S. Pat. No. 4,379,201 (Heilmann et al.). Initially, a mixture of monomers A and B is polymerized with a portion of a photoinitiator by exposing the mixture to UV radiation in an inert environment for a time sufficient to form a coatable base syrup, and subsequently adding a crosslinking agent and the remainder of the photoinitiator. This final syrup containing a crosslinking agent (e.g., having a Brookfield viscosity of about 100 centipoise to about 6000 centipoise at 23xc2x0 C., as measured with a No. 4 LTV spindle, at 60 revolutions per minute) is then coated onto a substrate, such as a backing. Once the syrup is coated onto a backing, further polymerization and crosslinking is typically carried out in an inert environment (i.e., an environment that is nonreactive with the monomer mixture). Suitable inert environments include nitrogen, carbon dioxide, helium, and argon, which exclude oxygen. A sufficiently inert atmosphere can be achieved by covering a layer of the photoactive syrup with a polymeric film, such as silicone-treated polyethylene terephthalate (PET) film, that is transparent to UV radiation or e-beam and irradiating through the film in air.
A preferred solution polymerization method for preparing a copolymer using monomers A, B, and optionally a crosslinking agent is disclosed in U.S. Pat. No. 5,073,611 (Rehmer et al.). Suitable solvents for such preparation methods include, for example, hydrocarbons such as benzene, toluene, xylene, normal hexanes, cyclohexane, as well as esters, alcohols, ethers, and mixtures thereof. For carrying out the polymerization in solution, some or all of the solvent is heated with some of the monomer mixture and some or all of the thermal initiator. When the polymerization begins, the remainder of the monomer mixture, and where relevant, the remainder of the thermal initiator and the solvent are added. After polymerization, the composition can be coated onto a backing and the solvent can be removed by evaporation with or without heat.
A latex polymerization method for preparing a copolymer using monomers A, B, and a crosslinking agent, is disclosed in U.S. Pat. No. 5,424,122 (Crandall et al.). For example, a latex emulsion polymerization is carried out by combining monomers A, B, and a crosslinking agent, an oleophilic nonionic free radical initiator, water, and a nonionic surfactant. The mixture is homogenized to form an emulsion followed by initiation of free radical polymerization, typically done using heat, while agitating the emulsion under an inert atmosphere. After polymerization, the latex can be coated onto a solid substrate and dried, typically at a temperature of at least about 65xc2x0 C. If necessary, water can be added or removed to reach an appropriate coating viscosity.
A pressure-sensitive adhesive composition may then be applied to the backing by a variety of coating methods including knife coating, slotted knife coating, or reverse roll coating. If the composition includes a solvent, it is then dried at a temperature (e.g., about 65xc2x0 C. to about 120xc2x0 C.) and a time (e.g., several minutes to about one hour) so as to provide an adhesive applique. The thickness of the layer of adhesive may vary over a broad range of about 10 micrometers to several hundred micrometers (e.g., about 200 micrometers).
Once the adhesive composition has been substantially fully cured and optionally crosslinked so as to provide an applique, the adhesive surface of the applique may, optionally, be protected with a temporary, removable release liner (i.e., protective liner) such as a paper liner or plastic films such as polyolefin (e.g., polyethylene or polypropylene) or polyester (e.g., polyethylene terephthalate) film. Such paper or films may be treated with a release material such as silicones, waxes, fluorocarbons, and the like. Only after the adhesive composition has been substantially fully cured and optionally crosslinked such that there is substantially no unsaturation are the adhesive appliques of the present invention applied to a substrate.
Optional Adhesive Additives
The acrylate pressure-sensitive adhesive compositions used in the appliques of the present invention can include conventional additives such as tackifiers, plasticizers, flow modifiers, neutralizing agents, stabilizers, antioxidants, fillers, colorants, and the like, as long as they do not interfere with the fluid resistance of the adhesive. Initiators that are not copolymerizable with the monomers used to prepare the acrylate copolymer can also be used to enhance the rate of polymerization and/or crosslinking. Such additives can be used in various combinations. If used, they are incorporated in amounts that do not materially adversely affect the desired properties of the pressure-sensitive adhesives or their fiber-forming properties. Typically, these additives can be incorporated into these systems in amounts of about 0.05 weight percent to about 25 weight percent, based on the total weight of the acrylate based pressure-sensitive adhesive composition.
Urethane Coating Layer
The cured urethane coating layers on the appliques of the present invention are made from the reaction products of a hydroxy-containing material (base material) and isocyanate-containing material (activator) for example, polyisocyanate. The curable compositions having the hydroxy- and isocyanate-containing materials may also further comprise a colorant. The curable compositions usually contain solvents and may also further contain other additives such as UV stabilizers, antioxidants, corrosion inhibitors, curing catalysts, and the like.
Useful stoichiometric ratios, based on equivalent weights, of isocyante: hydroxyl functionality are from 2.1:1 to 0.5:1, preferably from 2.1:1 to 1:1, and more preferably from 2.1:1 to 1.4:1.
The curing process can be accelerated by the addition of an appropriate catalyst. In general, such catalysts include heavy metal organic compounds; for example, dibutyl tin malate, dibutyl tin dilaurate, and naphthenate or octoate salts of heavy metals such as tin, lead, bismuth, cobalt, and manganese. Other suitable catalysts include tertiary amines and other nitrogen containing materials such as N-alkyl morpholines, N-alkyl aliphatics polyamines, N-alkyl piperazines, and triethylene diamine.
Inorganic and organic tin compounds are among the most effective catalysts for the reaction of isocyanates with hydroxyl-containing materials particularly alcohols and polyols. Tin compounds frequently employed for this purpose include stannous 2-ethylhexanoate (also referred to as stannous octoate), dibutyl tin dilaurate, dibutyl tin-bis(dodecyl mercaptan) and dibutyl tin oxide (DBTO). Other typical organotin compounds employed or proposed for use as catalysts or co-catalysts in urethane forming reactions are disclosed for example, in U.S. Pat. Nos. 3,582,501; 3,836,488; and 4,119,585. U.S. Pat. No. 3,392,128 discloses the use of dibutyl tin sulfonamide and U.S. Pat. No. 3,980,579 discloses a number of dialkyl tin thio-carboxylates. U.S. Pat. No. 5,089,645 discloses hydroxyl-containing organotin compounds useful as catalysts for the reaction of polyols and diisocyanates. Examples of commercially available catalysts useful in the present invention include FASCAT(trademark) 4202 and FASCAT(trademark) 4224 catalysts (both available from Atochem North America, Philadelphia, Pa.); and DABCO(trademark) T1 and DABCO(trademark) T12 catalysts (both available from Air Products and Chemicals, Inc., Allentown, Pa.). Useful amounts of catalysts typically range from 0 to about 800 ppm, depending on the formulation.
When dried and cured, the urethane coating layer provides a conformable urethane coating layer that has improved gloss retention and gouge and scratch resistance as compared to, for example, a fluoropolymer layer alone. Examples of useful commercially available urethane paints include a mixture of AWL Grip(copyright) #2 High Solids Polyurethane Topcoat Gloss and Hi-Cat #85 L/F Converter for High Solids Topcoats, available from U.S. Paint Corporation and DESOTHANE HS from Courtaulds Aerospace. Useful amounts of catalysts for the above commercially available urethane paints are from 0 to about 800 ppm and from about 250 to about 750 ppm respectively.
Preparation of Appliques
Appliques of the present invention can be prepared using standard film-forming and adhesive-coating techniques. Typically, a fluoropolymer is extruded onto a carrier, such as polyethylene terephthalate film to form a backing. The backing is then allowed to cool and solidify. The exposed surface of the backing is then treated to enhance adhesion of a pressure-sensitive adhesive layer. A layer of pressure-sensitive adhesive is then applied to the treated surface of the backing. A wide variety of coating techniques can be used, such as knife coating, roll coating, fluid bearing die, etc. The adhesive can also be applied using solvent cast techniques, for example. Alternatively, a layer of adhesive could be laminated to the backing. Thus, the adhesive can be polymerized first and then applied to the backing or it can be applied as a prepolymer and cured while on the backing. A release liner can be applied over the adhesive layer as described above. In some processes, it may be desirable to cure the adhesive through the release liner. The carrier for the backing is removed, and the exposed surface of the backing treated as described above to enhance adhesion to a urethane coating layer. The urethane coating layer may be applied using the same methods as described above for the application of the PSA. If the urethane layer is cured prior to application to the treated surface of the fluoropolymer backing, then PSA compositions described herein may be used to adhere the urethane layer to the fluoropolymer backing.
The outer exposed surface of the applique construction of the present invention may be provided with a patterned structure. Such patterned structures are useful for reducing fluid (e.g., air, water) drag resistance over and/or across the exposed surface. Such patterned structures and means of providing them are taught in U.S. Pat. No. 5,133,516 (Marentic and Morris) and U.S. Pat. No. 5,848,769 (Fronek and Kryzer). For example, a polymeric sheet (also referred to as a liner) having an embossed structured pattern on one surface may be laminated to the exposed surface of an applique having thereon a not yet cured urethane coating layer such that the urethane coating is in contact with the structured pattern. The urethane coating layer is subsequently cured with the liner in place, followed by removal of the liner prior to use of the applique. The result is an applique with a cured outer layer of polyurethane whose exposed surface contains the reverse image of the embossed structured pattern of the liner.